Add a new capability to RegisterContextLLDB: To recognize when the

Full UnwindPlan is trying to do an impossible unwind; in that case
invalidate the Full UnwindPlan and replace it with the architecture
default unwind plan.

This is a scenario that happens occasionally with arm unwinds in
particular; the instruction analysis based full unwindplan can
mis-parse the functions and the stack walk stops prematurely.  Now
we can do a simpleminded frame-chain walk to find the caller frame
and continue the unwind.  It's not ideal but given the complicated
nature of analyzing the arm functions, and the lack of eh_frame
information on iOS, it is a distinct improvement and fixes some
long-standing problems with the unwinder on that platform.  

This is fixing <rdar://problem/12091421>.  I may re-use this
invalidate feature in the future if I can identify other cases where
the full unwindplan's unwind information is clearly incorrect.

This checkin also includes some cleanup for the volatile register
definition in the arm ABI plugin for <rdar://problem/10652166> 
although work remains to be done for that bug.

llvm-svn: 166757

1 files changed, 7 insertions, 0 deletions

diff --git a/lldb/source/Symbol/DWARFCallFrameInfo.cpp b/lldb/source/Symbol/DWARFCallFrameInfo.cpp
index 5bd5dd50f75..7dbd7117a09 100644
--- a/lldb/source/Symbol/DWARFCallFrameInfo.cpp
+++ b/lldb/source/Symbol/DWARFCallFrameInfo.cpp
@@ -371,11 +371,18 @@ DWARFCallFrameInfo::FDEToUnwindPlan (dw_offset_t offset, Address startaddr, Unwi
     {
         unwind_plan.SetSourceName ("eh_frame CFI");
         cie_offset = current_entry + 4 - cie_offset;
+        unwind_plan.SetUnwindPlanValidAtAllInstructions (eLazyBoolNo);
     }
     else
     {
         unwind_plan.SetSourceName ("DWARF CFI");
+        // In theory the debug_frame info should be valid at all call sites
+        // ("asynchronous unwind info" as it is sometimes called) but in practice
+        // gcc et al all emit call frame info for the prologue and call sites, but
+        // not for the epilogue or all the other locations during the function reliably.
+        unwind_plan.SetUnwindPlanValidAtAllInstructions (eLazyBoolNo);
     }
+    unwind_plan.SetSourcedFromCompiler (eLazyBoolYes);
 
     const CIE *cie = GetCIE (cie_offset);
     assert (cie != NULL);